


Saccharine Shadows

by strawberrysummer



Category: Undertale (Video Game)
Genre: Ecto-Genitalia (Undertale), Explicit Language, Explicit Sexual Content, F/M, Nightmare Sans - Freeform, Rape, Reader-Insert, Slime, Tentacles
Language: English
Status: Completed
Published: 2020-01-19
Updated: 2020-01-19
Packaged: 2021-02-27 07:49:02
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 3,077
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22323601
Author URL: https://archiveofourown.org/users/strawberrysummer/pseuds/strawberrysummer
Summary: Nightmare can't stand the fact that no matter how hard he tries to make your life an unliveable hell, you just. Won't. Break.You're too persistent.Nightmare decides that it's time to take matters into his own hands.
Relationships: Nightmare sans/reader, Sans (Undertale)/Reader
Comments: 11
Kudos: 150





	Saccharine Shadows

**Author's Note:**

  * For [Moonie711](https://archiveofourown.org/users/Moonie711/gifts).



> AIGHT NYALL THIS IS PURE SIN AND MAJOR WARNING, IN CASE U DIDNT SEE IT BY NOW, THIS IS NONCON.
> 
> Disclaimer: This is a work of fiction and author does not think that rape is a good thing. (Gotta out this here cause apparently nyall can't handle a non-con fic existing and try to comment nasty shit at me??? Just don't read it man. As a trauma victim, let me expose myself and other willing participants to our trauma in a healthy, venting way. Ty.)
> 
> Anyways, for those of u who are ready, I hope u enjoy!!! I haven't written smut in a while so I hope it isn't to rusty for nyall. uwu lemme Kno what u think

Darkness always came so easily.

Whenever you lay your head, close your eyes, blink, for even just a moment; he is there. Always lurking in every corner, under every awning… wherever you look, you can find shadow.

It’s a part of everyday life, and yet no one ever thought to wonder what may lie beneath that surface, behind the silk veil of beyond and between. Anyone who did was shrugged off,  _ especially _ if they were to catch even a glimpse of what was behind.

This amused Nightmare.

He revelled in silent suffering the most; the ones that  _ knew _ how treacherous life could and would be to a human SOUL, but they never dared speak a word for fear of others lashing them with harsh words and dismissive replies.

You… you were one of  _ those _ . For weeks, for  _ months _ , he lurked. He fed into your emotions and allowed you to bottle them until they came bursting forth like a shaken soda can, and yet… Something about  _ you _ frustrated him beyond belief.

He tried to break you, surround you in a murky depth of sorrow and fear, and loneliness. For some reason, however,  _ you…  _ **_you…_ ** you still reached out. Cried for help. Went to a therapist and took your medication. You blamed your feelings and negativity on yourself and yet, never questioned when it would suddenly wax or wane.

Nightmare even resorted to most drastic measures: stealing those that you loved away. He never liked getting his own hands dirty, let alone killing, but for you,  _ you _ … he made that exception just a few times.

Even then, you never stopped.

His rage grew and festered, and he was incensed each time your pitiful little SOUL pieced itself back together and glued its wounds shut like a shitty, tenth-broken vase knocked out of its table for the umpteenth time.

He grew furious,  _ desperate _ , even. He changed tactics. He would let your depression simmer for a while, then suddenly boil. And then, when you thought it couldn’t  _ possibly _ get worse, he’d relent just slightly in a way that made your day better. He would let it evolve over the course of hours, then days, then  _ weeks _ … And when you had secured your faith in your emotions? He ripped. It all.  _ Away. _

**_He hated you._ **

Yet… You  _ still _ would not break. Your soul cracked and shivered, barely able to keep itself going, and yet…  **_you…_ ** you were Determined. Powerful.  _ Persistent. _

It drove Nightmare  **_insane_ ** .

Finally, on one of your worst nights, the dark entity that watched from your bedroom corner could stand to watch no longer. You clearly weren’t going to concede to his dark influences, so he had to take even more drastic, desperate measures. It had been such a long time since he’d had to resort to stepping in personally, but it would be worth it. Or so he hoped.

In the midst of one of your worst panic attacks, the looming figure finally left the corner of your room.

For a short while, he simply stood there, waiting for you to take notice and let loose some kind of shrill scream, like most humans did… if they weren’t paralysed with fear, anyhow.

Nightmare waited.

And he waited.

And he… simply waited.

Did you not notice how thick the shadows were? How low the temperature of your room had dipped? His rage made the windows frost and the atmosphere frigid; you could see your own breath, surely! 

_ How did you not  _ **_notice?!_ **

The longer he waited, the more impatient he became. He didn’t understand why you  _ simply. Weren’t. Looking up. _

Finally, FINALLY… You moved. Your spine straightened and your gaze lifted, falling upon him with a sheen over your irises that whispered still the stories of your tears. Nightmare’s breath hitched, and he didn’t realise he was holding it. The room darkened, became colder.

You didn’t scream.

This disappointed him, but his grin never faded, that thin sliver of white amongst goo and tar as black as the night sky. Instead of screaming, you simply regarded him as if he was an every day item in the corner of your room. His grin hitched higher, but his jaw was locked. You were finally looking at him and  _ not reacting at all! _ It infuriated him. What crimes would he have to commit for you to react with fear or loathing?  _ Something, anything! _

With a trembling voice, you…  _ spoke to him. _

“I wondered if you would ever show yourself,” you said, softly.

Nightmare froze in place, watching you as if you were a snake, ready to strike from that distance at any moment from your bed, somehow. He had heard your voice many times, and yet… never had the soft tremor of you fear been directed exactly toward him.

“I waited a long time, you know. I knew there was some kind of demon watching over me.”

The fact that you continued absolutely stunned Nightmare. You were trying to talk? To  _ him _ ? But… He hadn’t spoken to any human in years. Not in anything other than dark whispers, anyways.

The words came, regardless. His voice was dark, low; it bubbled through the tar as if it coated his vocal chords, should he have any.

**“Why are you not screaming?”** he questioned immediately, taking a few steps closer to see if you would react.

His singular, cerulean eyelight watched your expression and you just looked… exhausted. He could practically taste your fear, however, so it was an odd contrast.

“My voice hurts from crying,” you replied simply, taking him off guard. “Besides, screaming wouldn’t do me any good. None of the neighbors are home.”

Nightmare paused for a short while, thinking over that statement. He couldn’t help it, but he started to chuckle. It turned into a chortle, then a soft chuff… Finally, the entity’s laughter arose from his chest, loud and sinfully dark. Vicious and thick with malintent, the sound grated against your ears and filled your thoughts with shroud. You powered through, however. He seemed to be having fun, anyways.

**“You’re correct. Screaming** **_won’t_ ** **help you,”** he replied.

Before you got a chance to question him, Nightmare was upon you. You breath caught in your throat and you choked on a soft, fearful huff that did all it could to make itself known. It was the barest of noises, all you could make. His tentacles spanned much larger than himself or even your bed, easily filling the room with writhing, black tendrils that leaked tar onto your carpet.

It was one thing to see them, but once they laid upon your skin, your mind turned quickly to fear and disgust. You didn’t like the touch. It repulsed you to feel the slightly chilled serpents latching onto your limbs with their sticky ilk. Worse, was Nightmare’s face hanging directly over yours. That grin of his had turned manic, his single eyelight narrow and gleaming with months of repressed hatred. His breath was tepid, at best, and it smelled slightly of bitterness and apples as it washed over your lips and made the hairs on the back of your neck stand on end.

He was so close; you couldn’t help but wiggle and try to shrink away, but he was undeterred.

Nightmare’s tentacles tightened around your arms, bringing them above your head and pinning them to the mattress below you. Meanwhile, the dark tendrils around your legs gripped the limbs to near bruising, wandering farther upward than any stranger truly should.

The entity above you seemed to relish your terror once the chilly tar of his tendrils began searching for your most sacred warmth. He shivered, breath hissing out between his clenched, white teeth as he finally found it. A tentacle, still attached to your leg, rubbed itself insistently against your core. A choked cry of alarm finally left your lips, enticing a growl from Nightmare as he leaned ever closer.

His teeth crashed against your lips, bruising and insistent, violating the space between you as brutally as he felt like. Muffled noises barely escaped you in that mockery of a kiss, as his tendrils found their way past your undergarments and tested themselves against the warmth of your bared centre. It felt cold and wrong, but the stimulation was more positivity than you had had in  _ months _ .

The feeling of your slickened entrance and the slight dip of the level of negativity within your SOUL incensed Nightmare yet again. A beastly snarl left him and he didn’t hesitate to thrust a tentacle within your protesting, unprepared cunt. Your head tilted back and you let loose a scream, the penetration far more than you were ready for. Gasps of pain from the coldness suddenly entering and burning your depths forced themselves through your lips against his slightly ajar teeth.

The tentacle within you squirmed, as if happy to explore, prodding and rubbing against your tender walls. A moan left your lips, next, and Nightmare froze. He suddenly jerked his head back, a scowl on his face as he regarded your own. He looked disgusted with you, for making such a noise.

**“What’s wrong with you? Why are you enjoying it?!”** he hissed, his fangs bared just slightly as he pressed you further into the mattress.  **“No normal human being enjoys being violated, you disgusting cretin.”**

A whimpering laugh managed to make it through your clenched throat, and that only served for Nightmare to shove that tentacle deeper within you, earning him a pained, choked gasp. “You act like you haven’t been torturing me for  _ months _ ,” you mewled, biting at your lip as tears pricked your eyes. “You honestly think this is the worst thing you could do? It’s the only remotely good sensation I’ve had this entire time!”

Your defiance both enthralled and enraged Nightmare, and all he could think to do was simply continue with his efforts to make you suffer. Even though he knew now, that it wouldn’t work the way he had hoped. At least, perhaps, he could brutalise you and make you regret it if he was lucky.

**“What a freak,”** Nightmare muttered as he jerked the tentacle that was inside of you, suddenly freeing it from your surprisingly eager depths.  **“I suppose I got myself into this… but you’re going to regret it by the end. Don’t you worry, little human. I’ll make you suffer, still.”**

You took that as a promise, not a threat.

Nightmare leaned back suddenly, his hands diving to his clothing and tearing it aside in order to reveal a thick, cerulean cock that proudly sprung to life the moment he desired it to. Maybe he was… a little interested for the sake of his own pleasure. His hands took your panties, next, ripping them away with the pointed tips of his phalanges, the room briefly filling with the sound of shredding fabric. Your back jerked upwards just a bit against the grasp of his tentacles, your skin  _ painfully _ sensitive as his fingertips grazed your top, inner thighs.

The monster noted that reaction with a narrowed, calculating gaze, and decided after a few moments to claw his pointed phalanges down both of your thighs. Red welts were left in his wake, but no blood… not yet. Your whimpers intrigued him, further quirking his mood slightly higher into a more satisfied emotion.

**"What a naughty little human… Who knew that I would be in for such a treat, tonight?"** Nightmare's dark voice murmured, rumbling in his chest and thick with his cold ilk and arousal.

"Yeah, me n-neither," you managed to gasp out through the sensation, your tone biting and yet, somehow, sincere.

Needless to say, Nightmare didn't appreciate the sass.

He lowered himself over you once again, his tar-coated fabric and bones brushing your bare legs and making your shiver violently. One of his hands suddenly slammed down and twisted itself into the sheets near your head, his cerulean gaze cold, never leaving your face as he took pleasure in your fright response. His other hand wriggled its way underneath the over-sized t-shirt you had worn to bed, his frosty touch immediately causing gooseflesh to arise along your skin.

Nightmare leaned closer, toward your ear, his voice hissing and low and you felt the head of his cool member nudge against your heated entrance. His sharp fingers gripped at the tender flesh of your chest, lightly pricking the skin at certain points and causing you to softly whine.  **"I think… I'll allow myself to enjoy this. Very…** **_very_ ** **… much."**

The monster above you suddenly canted his hips forward, sinking the head of his length into your all-too welcoming core. You let out a shrill scream; this intrusion was  _ far _ larger than the last one. Nightmare ignored you, cruelly pushing forward and pressing further and further into the twitching depths he seemed so keen on taking his fun from.

His pleasured growls were quiet, yet low enough to be heard over your shouting and struggling. They vibrated against your chest even as his hand gripped your breast tighter, pushing you further into the mattress below. His and your breath, both, hitched as he slowly withdrew, the head of his member dragging excruciatingly against your walls. The pressure of his entering only returned more suddenly, this time, as he shoved himself forward again, much stronger than the last time.

Your breath rushed out of you, your stomach tightening instinctively as your urge to squirm away paused in order to deal with the pain. He was so much larger, stronger than you. What was the point of the struggle, anyway? He repeated the process again and again, this time earning cries that spilled from your lips as urgently as his powerful thrusts sent his cock delving into your soaking warmth, claiming and violating that sacred space within your body. With every movement.

He snarled into your ear as you moaned again for the first time, his anger at your enjoyance rising rapidly within his dripping, negativity-coated SOUL. After that, Nightmare didn't have any further patient with you.

His thrusts became more violent, more persistent. His girth forced you to stretch around him again and again, shaken cries and mewling leaving between the pained whimpers as the negative entity slammed into you repeatedly. Your bedframe creaked in protest at the animalistic movement as Nightmare rutted you into the bed, both of you enjoying the act in an instinctual, sickening way that your bodies both demanded you feel. You couldn't help it. What else were you supposed to feel? How could you resist? It was the only pleasure you had derived from Nightmare in so long that your mind was quickly filled with nothing but the image of him; the way he brutalised your weak, human body only eased his entry as your core slickened in response.

Nightmare lost himself to the feeling, ignoring your wanton groans in favor of harshly panting into your neck. His tar leaked all over your skin, your clothing, the bedding- it mattered not. The ilk found itself everywhere, just as his girth within you found every tiny spot that made you squirm and whimper.

**"That's it, human,"** Nightmare hissed, his voice shaken with how hard he sent himself into you again and again.  **"Nothing more than a slutty cocksleeve."**

The words nipped at your pride, tears pricking your eyes as a different kind of whine left your mouth.

Nightmare responded with a feral growl, his pleasure evident as his cold, wet tongue laved against the crook of your neck and trailed slime against your skin. He enjoyed the taste of the tears that rolled down your cheeks and neck as he continued to degrade you with various, cruel words and actions.

His hips canted yet again and he ground the head of his cock within your core, causing you to twitch and let loose a choking sob, overpowered once more by his growling. Your assaulter became invested in those noises, aiming to force them out of you again and again, as much as he could.

Despite his brutality, your pleasure continued. Likely not as much as his, however.

Nightmare found a spot that caused you to make the sweetest noises and he occupied himself with grinding into that spot within you, your walls twitching and shivering around his member as you thrashed against his tentacles out of instinct, your gasping and yowling music to his non-existent ears.

He couldn't say he was surprised, however, to be edging closer to his end. It had been a long time and humans were  _ oh _ so sweet. His panting became harsher, as did his thrusting, as he sought his own end. He didn't care about nor expect yours, and yet, it  _ came _ nonetheless. An enraptured snarl left Nightmare's maw as your walls clenched around him and he finally sank his teeth into the flesh he had been preparing with his tongue ages ago.

You moaned and trembled underneath him as the monster hilted himself as deeply as he could within you, his seed as cold and unforgiving as the rest of him.

Before you both could get too comfortable, Nightmare swiftly withdrew himself much to your body's chagrin. His release followed him out, leaking into your bedspread and joining the other various fluids that had collected during your coupling. You twitched there as he released you, feeling too light and too heavy at the same time at the loss of the weight of your restraints.

The entity admired your handiwork, although your fuzzy eyes didn't see his expression. You only jolted slightly as his hand roughly patted your cheek, mocking you with a false fondness that made your stomach curl in disgust.

**"How precious. You came… disgusting,"** Nightmare growled to you, but you didn't really seem to care all that much. You were on the verge of leaving this plane and diving into that of the sleep.  **"Don't worry… I think I'll be back to do it again. You make such beautiful art… I could almost take a picture."**

His voice held a feigned serenity to it and it didn't help your feelings of worthlessness. You were a mere toy to him, which didn't surprise you and yet it cut you like a knife, gutting any pleasure you had been forced to take from the activity.

**"Sleep and dream well, little human... I'll be** **_there_ ** **, too,"** his hissing voice followed you even into the realm of unconsciousness, something that would haunt your dreams for  _ years _ to come.


End file.
